1. Field of the Invention
The present invention is directed to position sensors, and more particularly to a two-dimensional inductive position sensing system using an arrangement of parallel inductors.
2. Description of Related Art
A variety of position sensors are known in the art. Examples include capacitance-based position sensors, laser-based position sensors, eddy-current sensing position sensors, and linear displacement transducer-based position sensors. While each type of position sensor has its advantages, each also presents disadvantages for some applications. For example, the size of capacitors can make their use impractical when the position sensor must be small in size. The same is true for linear displacement transducers. The complexity and/or cost of laser-based sensors and eddy-current-based sensors can negate their advantages in a number of applications.
More recently, U.S. Patent Publication No. 2011/0133727 disclosed an inductive position sensor using three inexpensive inductors arranged along a line. Briefly, the two inductors on either end of the linear arrangement are driven in series at the same frequency, but such that they generate opposing magnetic fields. The total magnetic field between them cancels at a central location, yet varies in a surprisingly linear fashion about the central location. The third inductor is used as a sensor to sample this magnetic field. The third (sensing) inductor is positioned between the two drive inductors and generates a voltage that is linearly dependent on the third inductor's position between the two drive inductors over reasonable translation ranges. However, the three aligned inductors define a one-dimensional inductive position sensor that is not sensitive to movement of the third (sensing) inductor off of the line that defines the linear arrangement of the three inductors. That is, if the third (sensing) inductor moves off the line that connects the outer two drive inductors, the voltage change caused by such movement is minimal thereby making it difficult to monitor an off-line motion or position.